Both scanning and transmission electron microscopy have vastly increased our knowledge of the various tissues and micro-organisms around us. However, conventional specimen processing have always produced artifacts or even changed the substructure of the organisms entirely. An environmental chamber which could allow visualization of the organisms in their natural state would be a very important innovation. Very few researchers have built environmental chambers for the SEM. Unfortunately, these chambers only fit the constraints of each individual microscope. Our overall objective for Phase I is to build a small, compact environmental chamber that will operate within most, if not all, scanning electron microscopes in operation today without major modifications to the microscope. The currently operational gas reaction stage will be modified into a prototype environmental chamber. This prototype will be used to determine the optimum size and dimensions for two differentially pumped apertures to allow pressures of 1 atmosphere to exist around the specimen. The study will continue to determine the size and shape of a scintillator-photomultiplier type backscattered electron detector that will yield the maximum signal detection, inclusion of a specialized specimen support for maintaining specimen viability, incorporation of a beryllium window for X-ray microanalysis and a thermoelectric device for accurate temperature control, and finally analyzing effects of different gases on the above features. Phase II funding will allow the construction of the stage according to the specifications found in Phase I and initiation of experiments on living organisms. An American microscope manufacturer has already expressed an interest in marketing the stage once it is operational.